I understand that you want to know if saving file in 'fmu' format genrerates 'xml' format along with it or not. In MATLAB, when saving a file in FMU (Functional Mock-up Unit) format, only the FMU file is generated. The FMU file contains the binary representation of the model along with necessary resources and data. It does not generate an XML file by default.
However, it's worth noting that the FMU format itself is based on the Model Exchange or Co-Simulation standards defined by the Functional Mock-up Interface (FMI) standard. The FMI standard does include an XML file called the Model Description XML, which provides information about the model's structure, variables, and other properties. This XML file is usually included alongside the FMU file when distributing models.
If you need the Model Description XML file along with the FMU file, you can generate it separately using MATLAB by using the FMU export options and specifying that you want to generate the Model Description XML. Refer to the following document for details: Export Simulink Models to Functional Mock-up Units - MATLAB & Simulink - MathWorks India
